Extreme Heat & Fertility in Nigeria

Nina Brooks

Cascade Tuholske, Kathryn McMahon, and Kwaw Andam

April 14, 2023

Motivation

  • Climate change is increasing the intensity, frequency, and severity of extreme heat events (IPCC 2023).
  • Impacts on fertility are understudied relative to other demographic processes but link directly to climate projections (Grace 2017; Kuehn & McCormick 2017; Sellers & Gray 2019).
  • Low-income, tropical countries face a triple burden (Grace 2017; Potts & Henderson 2012):
    • Climate vulnerability
    • High population growth
    • Poor with weak health systems

Evidence on heat & fertility relationship

  • Extreme heat exposure adversely impacts pregnancy outcomes, such as preterm birth, low birthweight, and miscarriages (Conte Keivabu et al. 2022; Davenport et al. 2020; Kuehn & McCormick 2017; Beltran et al. 2013)
  • Extreme heat reduces (Sellers & Gray 2019) or delays (Barreca et al. 2018) births in some contexts
  • Fertility preferences also impacted by heat exposure (Sellers & Gray 2019; Eissler et al. 2019)

Gaps and methodological issues

  • Many studies identify potential biological and behavioral pathways:
    • Biological: disease incidence, nutrition, infecundity, thermal stress
    • Behavioral: replacement, coital frequency, labor migration, income shocks
  • Critical exposure windows
  • Acute vs. chronic exposure and acclimatization
  • Differential impact of humid heat
  • Definitions of extreme heat exposure

In this paper…

  • We focus on Nigeria where hot-humid heat exposure has rapidly increased and fertility is high (avg parity of 4.4)
  • Examine effects of different definitions of extreme heat exposure on two fertility outcomes
  • Explore potential mechanisms

Data

Fertility

  • Two waves of Nigeria DHS with fertility calendar module (2008 & 2018)
  • Outcomes: conception, pregnancy loss
  • Restrict sample based on length of residence
  • Organize in “person-period” format for survival analysis

Heat

  • Combine CHIRTS daily Tmax record from 1986-2016 with relative humidity to approximate wet-bulb globe temperature (WBGT)
  • Spatially merge with DHS clusters
  • Construct several measures of heat exposure during each month (or trimester) of observation

Humid Heat Has Increased Along Geographic Gradient

Heat is correlated with conception probability

Humid-heat Increases Probability of Conception

Humid-heat Increases Probability of Pregnancy Loss


Heterogeneous Patterns For Conception

Conclusion & Next Steps

  • Preliminary results suggest humid-heat is associated with an increase in conception and pregnancy loss (in the 1st and 2nd trimesters)
  • Effect is concentrated among younger, less educated, and rural women
  • Continue exploring heterogeneous effects for conception and pregnancy loss to better understand potential mechanisms
  • Explore alternative definitions of heat exposure

Thank You!